Salt May Cause Even More Harm Than You Thought

New study finds that a salty meal reduces blood flow in your main arteries in just 30 minutes

The premise: Many experts insist that the most important line on a Nutrition Facts label is not the number of calories, but rather the sodium content. Salt has long been linked to an increased risk of heart attack and stroke, and high blood pressure. And it turns out, salt’s harmful effects kick in more quickly than we thought: A new study found that eating a single salty meal reduces blood flow in your main arteries in just 30 minutes.

The set-up: Researchers recruited 16 healthy adults and fed them each a high-salt version of tomato soup (containing 4 grams of salt) and later a low-salt version (made with just 0.3 grams). Each serving was about a cup. Before and after each round, the experts used an ultrasound machine to measure how smoothly blood was flowing in the brachial artery—the main blood vessel in the upper arm, which is normally used for checking blood pressure and gives an indication of cardiovascular health.

The results: After eating the salty snack, the subjects’ arteries widened only half as much compared to the results from the low-salt snack. (Blood vessel function is one of the earliest stages of fat accumulation, which can lead to blockages causing heart attacks and strokes.) The effect passed in about two hours.

Although the experts hypothesized that the higher salt meal would have an adverse effect on blood vessels, what surprised them most was that these effects were seen within just 30 minutes of consuming the meal. “We were also surprised to see that the salty meal produced similar effects on the blood vessel that we see after consumption of a meal high in saturated fats,” says the study’s lead author, Kacie M. Dickinson, a researcher at the Commonwealth Scientific and Industrial Research Organization in Adelaide, Australia.

The takeaway: Sure, the effects wore off within two hours, but repeated challenges to the lining of the blood vessel over time creates conditions that favor cholesterol sticking to the lining of the blood vessel. “This can lead to accumulation of fats in the blood vessel and, over the longer term, heart attacks and strokes,” warns Dickinson.

“On average 80 percent of salt intake comes from processed foods,” Dickinson says. “Many people are unaware of this fact and think that they eat ‘salt-free’ because they don’t sprinkle any salt onto their foods, which unfortunately isn’t the case.”

To help you better understand where your daily salt intake comes from, we talked to nutritionist Marissa Lippert, RD and author of The Cheater's Diet: “Some of your saltiest food culprits include an array of packaged or processed foods such as chips, fast-food menu items, canned and prepared soups, deli meats, frozen entrees and Asian takeout.” When making food choices at the grocery store and restaurants, Lippert says to always check the Nutrition Facts. “Aim ideally for 500 mg of sodium or less per meal or food item.” And keep in mind, the daily recommendation for sodium intake is 2300-2400 mg for the average healthy individual.